The invention relates to a method for providing a program module in a communications system, in particular in a radio communications system.
In present-day computer networks, a client/server structure is frequently used in order to provide new software, which is generally also referred to as a software upgrade. This client/server structure is distinguished by a hierarchical structure, with the software being stored in a relatively high-level server computer which provides the required software to client servers, which are connected to the server, when requested by these client computers.
Against the background of this basic model, which is also referred to as a single server architecture, there are further modified forms in which, for example, a plurality of servers process the requests from a large number of lower-level clients (multi-server architecture). So-called proxy servers may also be used for temporary storage of the software, and these are arranged between the client and the server in the hierarchy. The software which is requested by a client is temporarily stored in the proxy server in this architecture, so that, when it is requested once again by a different client, the software can be requested directly from the proxy server (which is generally located physically closer). This method is used, by way of example, for temporary storage of web pages that are called up frequently on the Internet.
In radio-based cellular communications networks such as the already existing GSM network (Global System Mobile), the planned UMTS network (Universal Mobile Telecommunications System) has a third generation mobile radio network or the Hiperlan/2 system as a future wireless LAN system, it is also necessary to carry out software upgrades, for example an upgrade to a WAP (Wireless Application Protocol) browser.
In this case, the software may be provided either by the manufacturer of a subscriber station, by a network operator, or else by an independent service provider.
In these methods, the connection between the server and a client is scrambled in order to distribute contents and software and/or program modules in a secure manner. Symmetric or asymmetric methods, such as PGP (Pretty Good Privacy) or SSL (Secure Socket Layer) are used in this case according to the related art. However, these methods have the disadvantage that they cannot prevent the contents and/or the software being modified by network components via which this information is transmitted to the subscriber terminal.
EP 0813132 A2 describes a method for distributing a program code, in which a trustworthy third party creates a certificate for the program code, which is distributed together with the program code. A receiving system can confirm the integrity of the certificate, and hence also the integrity of the program code, by checking this certificate.